Large refrigeration systems for industrial application routinely use oil flooded screw compressors for providing the necessary compression in the refrigeration cycle. Flooded screw compressors are well known and can be used in a wide variety of applications and with a number of different refrigerants. Typical refrigerants include ammonia, Freon and light hydrocarbons.
Circulating lubricating oil from the flooded compressors must be recovered from the effluent of the compressor and recycled to the body of the compressor in a continuous circuit. The design of refrigeration systems using flooded screw compressors is well known as is systems for reclaiming the used lubricating oil for return to the compressor. The majority of the reclaimed oil is taken directly from an oil separator with the small concentrations of the remainder of oil passing with the compressed refrigerant into a chiller. This small portion in the refrigerant is usually in the range of 10 ppm oil and needs to be recovered downstream to prevent the collection of oil in the refrigerant.
Prior art systems typically use an oil still to separate oil from the refrigerant and return the reclaimed oil to the compressor. In typical prior art systems oil is allowed to collect in the bottom of a chiller vessel and is then periodically batched with refrigerant into a still by manual or automatic control. An immersion heater evaporates the refrigerant in the still leaving the oil behind. The oil is transferred from the still and typically returned to the suction line of the compressor. The still operates in a relatively complex fashion and requires a level glass, high and low level switches, automated isolation valves and temperature switches to maintain its operation. Much of this equipment is needed to maintain proper operation of the immersion heater. Once recovered, oil from the still is typically pumped or pressured back to the compressor suction line.